Photometer.



UNITED STATES PATENT OFFICE.

ERNEST CSHING, OE BOSTON, MASSACHUSETTS, ASSIGNOR TO EASTERN ELECTRICCOMPANY, OE SAME PLACE.

PHOTOMETER.

SPECIFICATION formingpart of Letters Patent N o. 672,184, dated April16, 1901.

Application filed July 13, 1900.

To all whom, it may concern.-

Be it known that I, ERNEST W. CUSHING, a citizen of the United States,and a resident of Boston, in the county of Suffolk and State ofMassachusetts, have invented certain new and useful Improvements inPhotometers, of which the following is a specification.

In measuring the amount of light emitted by a luminous b'ody,.as anincandescent elec- Io tric lamp, it is customan'y to place the lamp tobe measured at a distance of five feet or farther from a lamp whichserves as a standard and in a straight line between them to put a diskof paper, in the center of which is a l5 grease spot. The relativeamount of light on each side of the grease spot is observed by the eyein a position at some distance from the line joining the two lampsthrough the grease spot by means of two mirrors, the whole forming theso-callcd Bunsen carriage. This carriage, consisting of disk, greasespot, mirrors, and a blackened box, with apertures for the entrance oflight on each side and for the eyes in front, is moved to the right orleft on the line between the lamps until the images of the spot in themirrors appear to be equally illuminated, when the relative amounts oflight emitted by the standard and by the lamp to be tested are indicatedby a pointer on a scale on the bar on which the carriage moves. Such anarrangement requires much space and is expensive, particularly when itis made portable, and has to be put together accurately and rigidly andset up in a room which must be dark and should have blackened walls.

I will now proceed to give a description of myimproveinen't, in whichthe drawings form a part, in which- Eigure 1 is a plan View of myimproved photometer with the cover removed. Fig. 2 is a sectionalelevation of the same, the cutting plane being on line z z on 1Fig. l.Fig. 3 is a cross-sectional view taken ou the line y y. Fig. 4. is aplan of the scale-slide. Fig. 5 is an end view of the latter, showingthe tube bearing the cord.

By the introduction of two mirrors f f at an angle in each case offorty-tive degrees the 5o light coming from the two lamps d e isreiiected to the grease spot a., so that the sources Serial No. 23,467.(No model.)

of light and the eye of the observer c are brought near together, andthe whole apparatus can be put in the box no, easily portable andblackened inside, thus saving weight, expense, and the need of ablack-walled dark room. The carriage being in this case immovable, thescale is marked on a plate which is attached to one of the lamps andmoves with it toward or away from the spot a. One 6o method ofconstructing a photometer according to these principles is shown in theaccompanying figures.

The box :1;,thirty-two by thirteen and onefourth by six andonehalfinches,inside meas- 65 urement, is divided by two longitudinalpartitions into a central space five inches wide and a space on eachside four inches wide. At one end of the central space is a centralpartition ten inches long having an aperture at a, 7o wherein is fixed adisk of white paper with a grease spot in its center. Atb b are twomirrors at such equal angles as to show reflections of the two sides ofthe disk and spot at a. to the eyes of the observer at c. Atffare twomirrors set in planes perpendicular to the floor of the box and at anangle of forty-five degrees to the plane of the disk. At j lo areapertures in diaphragms suiiiciently large to allow direct rays of lightfrom the lamps d e t0 shine on 8o the disk by reflection from themirrors f f, but sufliciently small to cut off confusing rays which arereiiected from the surfaces of the walls of the box and the partitionsin spite of their black surfaces. The sockets of the lamps d e areattached to bars of wood running in grooves, so that the lamps can bemoved forward and backward. In these bars may be tubes to carry theelectrical connections, as shown, or the electrical connections 9o maybe by ordinary binding-posts and wiring iu the box. On the upper surfaceof the bar carrying the lamp dthere is a scale g, divided so as to showa range of from tive to ten candle power, ten to twenty candle power,and twenty to forty candle power. When the line afd is just twenty-sixinches, the line on the scale 8, 16, 32 will be flush with the outsideof the box. The terminals `of the lamps are connected in multiple byexiroo ble cords with la socket 0, which can be attached to anincandescent-lamp bracket to supply current. In the circuit of the cordZ, leading to the lam p d, there are the usual connections for a slidingresistance, a voltmeter, and an ammeter or wattmeter.

The method of using this photometer is as follows: The socket 0 beingconnected with a source of current, a standard lamp (Z of approximatelythe same candle-power as the lamp to be tested and w-ith a voltage thesame or lower than the voltage of the circuit is put into the socketcland by the resistance introduced into Z the standard is brought to itsexact voltage and made to give its rated candlepower-say eight,sixteen,or thirty-two. The bar bearing the lamp is then so placed that the ratedcandle-power of the lamp appears on the scale flush with the outside ofthe box. Another lamp of approximately the same candle-power is put inthe other socket, and the bar carrying this lamp is moved in or outuntil the illumination of the two sides of the spot is exactly equal.The lamp at e is then at the voltage of the circuit, giving to the spotthe same amount of light as the standard lamp, and the lamp at e thusbecomes a standard for that voltage. The lamp at d is then removed, theresistance is cut out at l, and the lamp to be tested is put in thesocket d. By moving the lamp and the attached scale inward or outwarduntil the illumination of the spot is equal on each side thecandle-power of the lamp under test at the voltage of the circuit can beread on the scale ush with the outside of the box. Any slight variationsof the voltage of the circuit affects both lamps equally and aretherefore of little consequence. The watts consumed are read on thewattmeter or calculated from the reading of the ammeter in circuit at Z.The lamp d may be rotated by usual mechanism. (Not shown here.)

What I claim as my invention isl. In a photometer, having a white opaquedisk, and a translucent spot thereon,with two mirrors, one on each sideof said disk, and at such equal angles therewith as to reflect the imageof said disk and of the translucent spot thereon, at each side, to theeyepiece of the photometer, which is in the plane of said disk and on alevel therewith, and at a distance of about three feet therefrom, twomore mirrors, one on each side, and at equal distance on each side, fromsaid disk and spot, and in a plane in each case at an angle offorty-five degrees with the plane of said disk, and also at an angle offorty-iive degrees with the direction of the source of light whichilluminates said disk and spot, by refiection from said mirror, lastmentioned.

2. In a photometer, having a white opaque disk, and a translucent spotthereon,with two mirrors, one on each side of said disk, and at suchequal angles therewith as to reflect the image of said disk and of thetranslucent spot thereon, at each side, to t'ne eyepiece of thephotometer, which is in the plane of said disk and on a level therewith,and at a distance of about three feet therefrom, and two more mirrors,one on each side, and at equal distance on each side, from said disk andspot, and in a plane in each case at an angle of forty-five degrees withthe plane of said disk, and also at an angle of forty-tive degrees withthe direction ofthe source of light which illuminates said disk andspot, by reiiection from said mirror, last mentioned, a means of varyingthe distances of the source of illumination from the mirrors lastmentioned, as follows: two sliding bars, to each of which one of thesources of illumination is attached, and each bar fixed in such aposition that it may be moved forward and backward longitudinally, butis kept laterally in exactly the direction of a line having an angle offorty-five degrees with the plane of the mirror which refiects the lightof that source of illumination onto the said disk and spot described.

In testimony whereof I have affixed my signature in presence of twowitnesses.

ERNEST W. CUSHING.

Witnesses:

CHAs. E. TODD, ARTHUR P. CUSHING.

